(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "Red spider on cotton (Tetranychus bimaculatus Harvey)"

/ / 




1 



1'. S. DEPARTMEN1 OF AGRICULTURE, 

BUREAU OF BHT0M0L0GY- CIRCULAR No. 172. 

I < > I IOWARI >. I nlomolojri.l «nd Oriel ol IW.u. 



INK RKI> si'IDKI! ox COTTON 



e. \ McGregor, 

Entomolonii n\ 










BUREAU OF ENTOMOLOGY. 

L. O. Howard. Entomologist and Chief of Bureau. 

C. L. Mari.att, Entomologist and Acting chief in Absence of Chief. 

R. S. Clifton. Executive Assistant. 

W. F. Tastkt, Chief Clerk. 

F. H. Chittenden, in charge of truck crop and stored product insect investigation t. 

A. D. Hopkins, in charge of forest insect investigations. 

W. D. Hunter, in charge of southern field crop insect investigations. 

F. M. Webster, in charge of cereal <in<t forage insect investigations. 

A. L. Qttaintance, iu charge of deciduous fruit insect investigations. 

E. F. Phillips, in charge of bee culture. 

D. M. Rogers, in charge of preventing spread of moths, field work. 
ROLLA P. Currie. in charge of editorial icork. 

Mabel Colcord, in ehanje of library. 

Southern Field Crop Insect Investigations. 
W. D. Hunter, in charge. 

W. D. Pierce, G. D. Smith, J. I). Mitchell, Harry Pinkus, B. R, Goad, R \V. 

Moreland, A. W. J. Pomerov, engaged in CO I ton-boll weevil i n rest if/a t ions. 

F. C. Bishopp, A. H. Jennings, H. P. Wood. W. V. King, engaged in tick life- 
history in vestigations. 

A. C. Morgan, G. A. Runner, S. E. Crumb, D. C. Pabman, engaged in tobacco 

insect in vestigations. 
T. E. Holloway, E. R. Barber, engaged in sugar-cane insect investigations. 

E. A. McGregor, W. A. Thomas, engaged in red spider and other cotton insect 
investigations. 

J. L. Webb, engaged in rice insect investigations. 
R. A. Cooley, D. L. Van Dine, A. F. Conradi, collaborators. 
ii 



ADDITIONAL COPIES of this publication 
-ii- may be procured from the Superintend- 
ent of Documents, Government Printing 
Office, Washington, D. C, at 5 cents per copy 



Circular No. 172. taoedMaj 11 

United States Department of Agriculture, 

BUREAU OF ENTOMOLOGY 
L. O. HOWARD, Entomologist and Chief of Bureau. 



THE BED 8PIDEB ON COTTON. 1 

[Tetranychua bimaculatus Harvey.) 

By K. A. Mi(i nil, 

Entomological issittant. 

[NTHOD1 < TION. 

The minute reddish mite commonly know n as the red spider appar- 
ently i- becoming one of the serious enemies of the cotton planl in 

the United State-. It i- now prevalent throughout the cotton licit, 
and. especially in the last few seasons, has caused much alarm among 
the fanner- in certain sections. Seasons of excessive drought arc 
favorable to the development of the mite, and at such time- the pest 
increases 90 rapidly that the damage often becomes severe before it- 
presence i- detected. 

Red-spider infestation i< frequently miscalled "rust*' by farmers, 
since infested leaves soon turn deep red on their upper surface. Such 
leave-, however, if examined underneath, reveal the presence of the 
red spiders and the inconspicuous webs behind which they arc feed- 
ing and laying their eggs. 

HISTORY \M> DISTRIBUTION. 

With the exception of an outbreak in Louisiana, reported by Prof. 
II. A. Morgan in L893, severe occurrence of the red spider on cotton 
had not been rep. rted until 1903, at which time complaint- of dam- 
age came from South Carolina and Georgia. In 1904 Mr. I-'.. S. G 

1 This firruinr i* baaed primarily upon work done :it Batesburg, s C, in 1911 and 1912, 
under rh.> direction of Mr. W. l» Banter, bat also Include* the results o( uuaenal 

<;. a. Runner and 11 f. Wilson daring the two preceding seasons, it - 
»f and ■opersedes Circular No. !■"". 

1 



THE RED SPIDER OX COTTON. 



Tit id-, then of this bureau, found severe infestation in fields about 
Batesburg, S. C, and the following year he reported severe injury 
in North Carolina. South Carolina. Georgia, and Alabama. Since 
then the additional records of Dr. F. II. Chittenden and Messrs. 
G. P. Weldon, D. T. Fullaway, and others, as well as the writer. 
have established the presence of this red spider from Maine to Flor- 
ida and westward to California and in the Hawaiian Islands. With 
the exception of western Colorado and portion- of California no 
complaints of an alarming nature regarding this pest have come to 

the writer's attention other than from 
the southeastern portion of the cotton 
belt. It is here that the red spider ap- 
pears to have found the conditions most 
suitable for its development. 

The red spider was described by Har- 
vey in 1893 as Tetranychua 2-maculatu8. 
Harvey considered it quite distinct from 
the European species T. telarius L. His 
types were from Orono. Me. In 11)07 
Prof. H. A. Morgan published observa- 
tions on the cotton mite, and apparently 
accepted the determination of the species 
as T. telarius. In 1D00 Mr. Nathan Banks 
described the cotton mite under a dis- 
tinct name — Tetranychua gloveri — but 
from the study of additional specimens 
has now concluded that the name is 
synonymous with Harvey's T. bimacu- 
latus. Specimens of red spiders on cotton 
from South Carolina have upon two re- 
cent occasions been determined by Prof. 
A. Berlese as the continental specie: — 
Tetranychua telarius. As there seems to 
be considerable doubt on this point, we shall follow Mr. Banks 
in considering the form with which we are dealing as Tetranychua 
bimaculatus. 

DESCRIPTION. 

The typical female (fig. 1) is 0.50 mm. long by 0.26 mm. wide. 
broad-oval, widest in front, and the legs are shorter than the body. 
Its color is usually brick-red. The typical male is 0.27 nun. long by 
0.1.") mm. wide, oval-wedge shape, narrowed behind, the legs about 
equaling the length of the body, and its color i- usually reddish 
amber. Individuals of both sexes usually possess on either side of 
the body a dark spot, caused by the food contents. This -pot may 
vary greatly in color, size, and outline. Similarly, depending upon 




Fig. i. The red spider, Tetrany- 
rlnis Mmaculatus: Adult fe- 
male G r e a t 1 y enlarged. 
i From Banks, i 



I ill i;i D BFIDI R ON COTTON. •'. 

the host plunl and upon locality, the general color of the red spider 
i- subject i o great * ariat ion. 

I'lu' egg are ven minul ■. but in proportion to the mites the} are 
large. 1 1 n- \ are perfectly round, and when first laid are as cleai i 
water. Bach female lays (in the months of June, July, and August) 

about .'in to 60 eggs, although her br I may in cases exceed 100, 

[Tsualh about G i^^- are deposited \»y da} for a period of fl or 10 
days. Less than •'• eggs or more than I" are rarely deposited in one 
day in summer weather. During the warmer months the eggs hatch 
in about I daj - a fter being laid. 

The newly hatched red spider, called the larva, is almost round, 
has six legs, and is nearh colorless. Ii begins feeding at once, and 
i in summer time) after two days 1 activity it becomes quiet, darkens 
in color, casts its skin for the first time, and emerges as the primary 
nymph \\ ith an added pair of legs making eight. 

The primary nymph becomes larger in size and darker in color, 
I ii it gives no indication of sex. Feeding continues actively, and at the 
termination of another two-day period i in summer months) :• second 
molting occurs, which gives rise to the third stage the secondary 
nymph. 

With this last nymphal stage the first indication of sex appears. 
As with the preceding stages, two days usually suffice in summer 
for the completion of this period, at the end of which time the 
skin is shed for the third time and at last the perfectly developed 

adult mill'- appear. Ai il :currence of each molt the skin splits in 

two, crosswise, and tin- creature crawls out of the two halves. The 
old cast skins are usually t<> be seen in abundance among the fibrils 
of the \\ eb. 

I III \DI M \I \I l - \\n FEMALES COMPARED. 

Concerning the relative abundance of females and males it may !>»■ 
said that there seems to be n predominance of females throughout 
the summer, but toward the approach of cold weather the occurrence 
of the sexes becomes more nearly equal. The period of life of the 
.•idult female varies from 1" tiny- in midsummer to several months 
in winter. The male is shorter lived. A- before stated, the female 
i- decidedly larger than the male, more rounded behind, and of a 
much deeper color. She does n< >t move about much, and when she 
■ loo- her motion is rut I in- slow. < hi the other hand, when not mating, 
the male is frequently seen moving rapidly about. The body and 
legs are well beset with bristles, which are -"mew hat more con 
spicuous in the male- than in the females. In addition, the legs of 
the male are longer in proportion to the body than are those of the 
female. The legs of the first pair are especially long in the male, and 
are doubtless adapted for clasping. The ey< -. consisting ea< h of two 
orbs, one close behind the other, are situated near the front edge of 
the body directly over the second pair of legs. 



THE RED SPIDER ON COTTON. 



MATIXO. 



Almost immediately upon becoming adult, the red spiders mate 
and begin egg laying. The males seem to recognize unfertilized 
females with ease. The first eggs are frequently deposited on the 
same day upon which the transformation occurs from the last 
nymphal to the adult stage. 

PARTHENOGENESIS. 

Experiments conducted with unmated female red spiders clearly 
prove that they are normally capable of laying eggs, which in turn 
hatch and develop into mature individuals. Xo tests, however, have 
been successfully conducted to determine the sexual fertility of the 
latter. 

GENERATIONS. 

The season of 1911 at Batesburg, S. C, was one of unusual drought 
and heat, and there were about IT generations between March 11 and 
November 5. The time required for a single generation varied from 
35 days in March and early April to 10 days throughout most of 
.Tune, July, and August, and to 25 days in the greater portion of 
October and early November. During the same period of 1912 at 
Batesburg only 1G generations were produced. The 1912 season 
was late in commencing, was somewhat cooler than that of 1911, and 
more showers occurred. From April 24 to September 25 there was 
small variation in the time required for the generations — averaging 
about 11 days. Two generations developed each in 9 days, which is 
less than was required for any brood in 1911. Thirty days was re- 
quired for the October-November generation. The following table 
presents the duration of each stage of each of the 17 generations 
for 1911 : 

Table I. — Development of veneration* of tin- nil spider on cotton in 1911. 



Gener- 
ation. 



Period covered by generation. 



Incuba- 
tion 
period. 


Larval 
period. 


Nvmph 

"(1) 
period. 


Days. 


Days. 


Days. 


13 


9 


6 


6 


3 


3 


6 


3 


3 


5 


3 


2 


5 


3 


2 


4.5 


2.5 


2 


4 


2 


2 


4 


•> 


2 


4 


2.5 


2.5 


4 


2 


2 


4 


2 


2 


4 


2 


) 


5 


2.5 


■> 


5 


2 


2 


5 


3.5 


3 


>; 


A 


A 


9 


6 


5 


5.5 


3.1 


2.7 



Xymph Ovipo- 
i2i sit ion to 
period. adult. 



1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
17 



Mar. 11 to Apr. 14. 
Apr. 15 to Apr. 29. 
Apr. 30 to Mav 13. 
Mav 11 to May.'.",.. 
May 26 to June 6.. 
June 7 to June 17.. 
June is to June 27. 
June 28 to July 7.. 
July 8 to July 18.. 
July 19 to July 28. 
July 29 to Auj;. 7.. 
lug. B lo Aug. 1 , .. 
Aug. is to Aug. 29. 
A.ug.30toSept.9. 
Sept. 10 to Sept. 24 
Sept. 25 to Oct. io. 

Oct. 11 to Nov. 4.. 
\verage 



Days. 



2 

2 

2 

2 

2 

2 

2 

2 

2 

2.5 

2 

3. a 

4 

5 



Days. 



35 
15 
14 
12 
12 
11 
10 
10 
11 
10 
10 
10 
12 
11 
15 
16 
26 



2.8 



I ii I Kin BPID1 i: ON ' 01 l<>\". 5 

le 1 1 indicates the duration of, and the period covered by, each 
of tlir it, generations for 1912 ;i- well at for the 1911 12 wintering 
era I ion. 

I.I || / I, l i h, /il, 1 1 ill ,,! : il' Hi l H I I'm - .■• ./hWi , .,</ i nl Inn in I''! ' 





M 

ia 
ta 

ii 
ii 
i a 
i-' 
ii 




Hon 


\n 1 191] to \ 






\i>r 




in 


■ 











10 




i 


ia 






17 




■ 




1 to Jill \ 1 1 






Jul' IS to Jul \ .'I 













■ * Intering nil itaoold I 

km \iin\ OP w I v 1 ill 1 : I" BREEDING \' ITVITIES. 

The influence of the weather on breeding activity is ven notice- 
able. Hot, dry conditions greatlj favor and hasten development, 
while cool, wet weather correspondingly retards it. A female laying 
normally about 6 or 7 eggs per day will often upon the occurrence 
of .i very hoi day suddenly increase the number to 15 or even more 
eggs per day, or upon a chilly day may drop ;i- suddenly to 1 or -1 
Ii i> easy then to understand the remarkable rate al which 
this pest increases during times of unusual drought. 

OBSERVATIONS on HABITS. 



Iii establishing herself upon cotton the female selects a concave 
area between the under veins of the leaf and begins ;it once to deposil 
eggs. These may be attached to the fibrils of the web slightly above 
ilic surface, or, as seems mosl often the case, they are placed directly 
upon the leaf. The eggs are usually clustered rather closely and 
rarely occupy an area greater in size than that of a dime. Feeding 
continues interruptedly throughout the period of egg laying, and the 
affected area of the leaf becomes thickly dotted with the blackish- 
green puncture marks. Meanwhile ;i wine-red spol has appeared on 
the upper surface of the leaf directly over the young colony, which 
spreads ;i- the colony increases and may finally color the entire leaf. 
A> the eggs hatch the larva? remain close to the place of their birth. 
The mites seem to U- decidedlj gregarious. In n young colony 
there is usually little web formed, bul where the spiders are veri 
abundant the web may become quite conspicuous. It doubtless 
affords some protection from adverse weather conditions, as well ib 
.i ir:i : n-t hostile intruder-, since upon several occasions predaceous 



THE RED SPIDER ON COTTON. 



insects have been observed ensnared and dead among the fibers. New 
females, after mating, either select an attractive --pot on the leaf, 
or migrate upward to a more tempting leaf, or, as frequently is the 
case when overcrowded, travel to another plant. 



THE VIOLET AND POKEWEED AS HOSTS. 

When cotton dies or becomes un tempting in the late fall an exodus 
of red spiders from the cotton fields occur- in the effort to find more 
suitable food plants. At this time cotton mites may be easily found 
on a number of native and cultivated plant-, prominent among which 
are cowpeas, tomato. Jamestown weed, ironweed, pokeweed, and cul- 
tivated violets. Most of these plant- die after the frosts, but poke- 
weed furnishes considerable green tissue beneath the ground level. 

and the violet remains somewhat green 
throughout the winter. Out of many 
case- of cotton infestation investigated 
during tin- last two seasons the rast 
majority of them have indicated 
most clearly that the original source 
of the pest was either the English 
violet (figs. •_'. 3) or pokeweed [Phyto- 
lacca <1( candra) (fi<r. 4). 

Practically all occurrences in urban 
localities have been intimately associ- 
ated with cultivated violet plants and 
doubtless originated from them. On the 
other hand, with very few exceptions 
rural case- of infestation are traceable 
to pokeweed -talks growing at the 
field borders or on the terraces. The 
description of a rural occurrence at 
Allendale. S. C. will serve to illustrate a typical case of origin from 
pokeweed. In this instance the infestation was seen to grow increas- 
ingly severe as one approached a certain point on a terrace. Con- 
verging from all directions toward this center, infestation clearly 
became heavier until an area was reached where the plants were de- 
nuded of foliage. Precisely in the center of this area there grew a 
large pokeweed stalk. It was "alive" with mites and was lightly 
festooned with their webbing. 

It is not yet entirely clear in what maimer the red spider passes 
the winter on pokeweed. The plant i- a perennial, and the stalk- die 
to the ground in the late fall. Just below the soil surface, however, 
the soft fleshy roots, which are succulent, begin (fig. 4). In addition, 
at the crown of the root, at about the ground level, there are always 





: : -i-V: ':■■;■':: 






o O O 






o 






o 






• □ 





Fig. 2. — Diagram showing how vio- 
lets growing in dooryard give 
rise to red-spider infestation in 
adjoining field. The infestation 
is most severe near tli" yard. 
This diagram is typical of many 
cases found during 1011. (Au- 
thor's illustration, i 



I 11 I. Ill l> -. I • 1 1 • i I: i'\ COTTON. 



to be found through the winter months the tender dormant bud.s 
which give rise t<> the stalks of the following season. Upon Novem- 
ber 23, 1912, following -«-\ **t;i I severe fro ts al Batesburg, S I 
few uf the mites were seen, apparently feeding on these winter buds. 



mi in i; 1 1 « • — i — . 



A- a result of the investigations at Batesburg. together with tin' 
earlier observations <>l the red spider mi cotton, tlii- mite has been 
seen upon over 90 species of plants, including weeds, ornamental 
plant-, ami garden and field crops. Upon most of these the pest has 
,inlv occasionallv been seen, '"it it has been found commonlv through- 




■ pica I * lolel bo 
plants constituted the son m which resulted In the - in of a 

mall i > otton Beld direct I j a< r — the • 

out the active season upon the following plant-: Beans, cowpeas, 
dahlia, ironweed, Jerusalem-oak weed. Jamestown weed, okra, tomato, 
wild blackberry, wild geranium, pokeweed, and English violet. \1 
Brownsville, S. ('.. Augusl s . I'.M-j. a case was seen where a field of 
corn was immediately adjacenl to a badly infested cotton patch. The 
infestation had spread into the corn and the cowpeas growing be- 
tween the corn rows. One-fourth of the corn had been pulled up 
ami the balance was very severely infested. Many of the cornstalks 
exhibited large rusty-yellow blotches on their blades and, in fact, 
had the pesl appeared when the corn was younger it probably would 
have ruined the <rop. On the cowpeas the infestation was heavy. 
many of the leave- had dropped, and those remaining were discolored 
and distorted, 

78463 Or. 172 18 2 



THE RED SPIDER ON COTTON. 
HIBERNATION VERSrS WINTERING 



Some observers have thought that the red spider commonly hiber- 
nates in trash or in the soil in cotton fields, but the investigations in 
South Carolina have produced absolutely no evidence to support this 
idea. During the late fal] and early spring, when the weather was 




Pig. i System of Besby roots of the pokeweed (Phytolacca decandra), showing the 
attractive winter buds at about the ground level, ;is indicated by the dotted line. 
i Original, i 

as cold as it becomes in South Carolina, trash has been taken several 
times from fields in which the infestation had previously been severe 
and examined with great care. A few minute dormant acarids and 
other forms have thus been obtained, but no red spiders have been 

found in such material. 



Ill I. i;i I' SPIDI H ON COTTON. 






Thai ilii> pesl remains more or less active throughout the winter 

there can be loubt. Mr. <> \. Runner f< I active adults al 

Batesburg, S. C, <>n December 21, 1909. Mr. II. I . Wilson observed 
red spiders feeding In earlj February :ii the same locality, rhe writei 
found ;ill stages alive on English violets on March LI, and adults 
late as December L9 al Batesburg on the same host in 1911. Adults 
were seen alive on violets al Batesburg on February 23, 1912. follow 
Ins the coldesl winter thai section had experienced for mam years. 







V. 1 


\* 5:1 


f^r w 






■ 



An uninfested cotton plant, - Id as shown In I 

beyond the boundnrj of Infestation bj the red Bplder. 

The finding of the active red spiders during the coldesl weather is 
certainly an additional indication thai hibernation does nol take place 
in South Carolina. 

DISPI RSIOX. 

How do red spiders become established upon cotton? They have 
no wings and theii legs are very minute. Cloa observations n 
that on the ground they normally travel at the rate of 1 inch per 
L5 seconds, which, it' maintained, would total -l v|1 feel in 24 hour-. 
Red spiders are doubtless occasionally transferred by dogs, chickens, 



10 THE BED BPIDEB ON COTTON. 

other domestic animals, insects, and bird-. Strong winds may serve 
occasionally to transfer them from plant to plant. It i- the writer's 
firm belief, however, that the chief means of dispersion is the red 
spider's own efforts. When once established in a field they may be 
further distributed by farm hands and by stork while cultivation is 
being carried on. They also spread from plant to plant along the 
interlacing branches, but trap- specially prepared with tanglefoot 
and placed in the Held have proven that individuals commonly crawl 
from plant to plant by way of the stalk and the ground. 

Since the red spider apparently uses no instinct or intelligence in 
finding cotton plants, it follows that the pest must hit upon the cotton 
stalk- entirely by chance. The result of this haphazard manner of 
migration must necessarily result often in the penetration of the 
spiders far into the center of fields, thus giving rise to the mistaken 
impression that they had hibernated at these point-. 

Furthermore, as the likelihood of the discovery of cotton by the 
spider is doubtless in proportion to the thickness of the " stand." it 
should follow that the thick broadcasting of a narrow border strip 
along the edge of a field adjoining a source of infestation would serve 
as a trap crop to intercept the majority of migrating spiders. This 
strip should be plowed in as soon as there seems to be danger of a 
general movement to the main field. (For a practical test of this idea, 
see under Prevention, p. 17.) 

There is an old adage which has come to the writer's attention 
several times the past season from the lips of old planters: "When 
the pokeweed turns red, look out for the cotton ' rust." ' This ex- 
pression, said to have been employed in antebellum days, is of con- 
siderable interest, since it contributes evidence tending to prove the 
long existence of the cotton mite in the South, as well as the function 
of the pokeweed. 

TIME OF APPEARANCE AND DISAPPEARANCE. 

In 1911 the work of the pest on cotton first became noticeable about 
June 1 at Batesburg. The past season (1912), however, red-spider 
work was not evident on cotton until about the last of June at that 
locality. From the answers to a large number of inquiries sent to 
fanners throughout South Carolina, the average time of first appear- 
ance in fields the past season is found to have been June 30. The lower 
(sandy) section of the State averages one-half month earlier in the 
pest's arrival than does the upper (clay) section — June 2."> marking 
the arrival time for the former and July 10 for the latter. Although 
the pest does not become readily noticeable on cotton until some time 
in June, it really establishes itself considerably earlier. Mites have 
•asionally been seen by the 1st of May on seedling plants not over 



Ill I 1:1 i' -I'lhl i; ON COTTON. 



11 



'_' inches high. In both l'-'ll and 191j2 the pesl abandoned cotton 
about the Insl of August. This makes the period of activity cover 

:i I >< ii 1 1 12 w ceks. 

\ \ n 1:1 • .1 |p \ M m.i . 

The presence of the pest <>ii cotton is first revealed by the appear 
a nee on the upper surface of the leaf of a blood red spot. A- leaves' 
liecome l>adl\ infested ihe\ redden over tin* entire surface, become 





,i. Cross section of normal cotton leaf; <>. cross section ol cotton leal Injured 
tii.- red spider. The puncture Is near lower right-hand corner. Highly magnified 
i tatbor'a Illustration I 

distorted, and drop. Figure 5 shows an uninfested cotton plant for 
comparison with figure 7. infested. The lower have- usually are first 
attacked, but infestation spreads upward until often only the bare 
stalk and one or two terminal leaves remain, i Sir fig. s . i Such 
plants almost invariably die. The injury to the leaf and the dis- 
coloration which follows the feeding of the mites are easily under- 
stood by referring to figure 6, winch represents (a) the appearance 
of healthy cotton leaf : tissues and (6) the condition of the tissue 
after feeding by the pest. As previously intimated, the worst spots 
of infestation arc cither to be found in close proximity to yards with 
Ixtrders of violets or to a clump of pokeweed stalks. Large fields are 
probably never completely damaged, bul -mailer fields frequently 
become wholly affected. A thorough examination of all fields within 
1 mile of the center of Leesville. S. C, was made with a view of detei 
mining the exact status of red-spider infestation at one specif] • 



12 



THE HED SPIDEB <>N COTTON. 



locality. In all, 99 fields were examined as carefully as possible. 
The following table presents the result.-: 

Table III. — Results of mi investigation to determine th< degree of infestation of 
cotton by the red spider at Leesville, 8. <'.. 1912. 



Number 
Degree of infestal Ion ol fields ex- 
amined. 


Per cent 
of total 
fields ex- 
amined. 


Very acute i x 

Very considerable 20 

Slight 35 

None 26 


is 2 
■l- 1. 2 
35. 3 
26 3 


Total 99 


100.0 





Total number of fields visited 

Total number of fields infested " : * 

Average percentage of infestation for the community \.'i 




In;. 7. — Cotton plant in an early stage "f 
infestation by the red spider. Many leaves 
are discolored and some of the lower ones 
have dropped, i Original. I 



p 1G s. — Cotton plant in well ad- 
vanced stage of infestation by the 
,-ed spider. Nearly all le 
squares, and bolls have been shed. 
1 1 iriginal. > 



This occurrence was one of the 
at any time come to the writer's 
case in this locality (and one of 
had its origin in a large clump 
at the edge of town (fig. 9). 
reached in one direction a point 
final affected area, semicircular 
within its confines the occurrence 
litis was unusual. 4-aav or 5-acre 
age, arc frequently to be seen. 



severest and most general that has 
attention. Perhaps the most severe 
the worst yet seen) was one which 
of badly infested pokeweed stalks 

The pest spread fanlike until it 
GOO feet from the pokeweed. The 
in shape, comprised 13 acres, and 
was general. While such a case as 

spots, with 25 to 100 per cent dam- 



I II I RED 



i • 1 1 ' I i : O > i ii I 1 1 1 N . 



13 



NATl'RAI ' • i\ l in il l l m. \i.| m 1 1 -. 

In both the seasons of L911 ami 1 ■ > I _' red spider occurrence wa 

~i severe throughout July and earlj August. The last two week 

of August in both cases, however, witnessed so greal n reduction of 
the pesl that l>\ the end of thai month il was hardl) noticeable, 
:i rule. This phenomenon, indeed, happens suddenly, and the agen 
cies which work to produce il are unquestionably of greal economic 
value. The ageing and toughening of the leaves al aboul this time 
ni;i\ cause many mites to desert the cotton for other plants, but 
another factor of probably much greater importance is the increased 
abundance of several species of insecl enemies which seem to gain 
dominance nl jusl this time. 










m, 








« 










A-P] 








1 •'•' 

1 


- ■ t - 


£**** 


• i 


A* 


L ?i . 


.•» 


>-* 



i \ severe example oJ red-spider work In a cotton Held N'enrlj all plant* In the 
I nre In the i ondll loi 8. 1 ertaln 

I ■ . . k < - \\ • -i d stnlkf 
lllnst ration. (Original i 



i MM \ I H' IMI I I M 1 -. 



\- before mentioned, climatic conditions exert a marked influence 
upon the welfare <>f the pest. During times of little rainfall and 
high temperature reproduction goes on h\ leaps and bounds; on 
the other hand, long, heav^ rains work havoc to the red-spider 
population. In spite of the fad that the red spiders inhabit the 
underside of the leaves, many are washed off by rains and many more 
are destroyed by the upward bombardment of -and particles, which 
may always be seen coating the lower leaves after storms. In fact. 
it appear- true thai a few heavy rain-, especially if they continue 
for -mne time, accomplish as much toward controlling the pest as 



14 



Till'. I',K1) BPIDEB ON COTTON. 



anything which can 1m> done by man during the season. From obser- 
vations made, both early in the season and at the beginning of win- 
ter, it is doubtless true that the young stages are killed by freezing 
weather. This naturally prevents any considerable winter increase, 
and in addition some adults probably perish. 

The influence exerted upon the red spider by preseasonal condi- 
tions appears to be even greater than that of the factors operating in 
summer weather. The winter of 1J>11-12 was the severest in South 
Carolina for many years. Hence it might be expected that the fol- 
lowing season would be a mild one. from the standpoint of injury 
l>y the red spider, through the assumed heavy mortality of the pest 
during the winter. On the contrary, as has been stated before, the 
1912 occurrence was the severest on record. The only possible ex- 
planation appears to em- 
brace two suppositions. 
One is that the adult red 
spider is little susceptible 
to extreme cold. The 
other is that the insect 
enemies of the mites suc- 
cumb much more easily 
to minimum temperature- 
|i» // v~-# than do the mites them- 

selves. Both of these hy- 
potheses are sustained by 
all observations of the 

Fig. l&.—ArtJvrocnodai s,,.. a predaceous enemy of writer. .Naturally, then, a 
the red spider. At left, mature predaceous larva, severe winter is precise! v 
magnified 60 times; at right, adult female, greatly 1 ± 1 1 <• 

enlarged. (Original.) " what W<mld mOS * fav ° r 

the subsequent increase of 

the red spider through the destruction of its insect enemies. Con- 
versely, an abnormally mild winter, free from decidedly low tempera- 
tures, should furnish conditions most favorable for the survival of 
the repressive species, and the infestation for the following season 
would be mild. 

INSECT INI MM s. 




Hot weather, although favoring red-spider development, probably 
encourages even more the increase of insect enemies, of which sev- 
eral have been observed. Were it not for these inconspicuous friends 
of the farmer the depredations to his crops by the red spider would 
unquestionably be more severe. The following are a few of the 
more important beneficial species observed during the season of 1912 
at Batesburg, S. C. 



I n I BED SPIDER ON COTTON. 



I.". 



Wthrocnodax sp. 1 (fig. LO). Dunn- the =eae I 1912 a species 

f \rthroonodnx, a ft} belonging to the familj Itonida I formerl) 
I ulomyiiilw). was first noticed toward the last of June, a1 which 
"„:,, ,,,,i ;,i all common. It increased wrj rapidly, ho* 
ever , an d l.\ the end of Juh had become quite abundant, li is the 
larva (grub stage) of this insecl which assists the farmer, and the 
attack seems to be limited entirely to the red-spidei I ming in 

contacl with an egg, the larva instantly thrusts its piercing organ 
through the shell and begins to feed. Large Larva; will dev< 
egg in from one to two minutes, while the smaller larva? require 
more time, according to their size. When mature, the larva spins 
a woolh cocoon 1 mm. 

in length. The adult 

llx issues after a brief 

pupal stage, and the 

full generation requires 

little time. This insect 

i^ probabl) the mosl ef 

fective enemj of the cot- 
ton mite, and to its final 

superabundance is prob 

:i!)l\ largely due the 

late summer decimation 

of the red spider. It 

has been recorded from 

the follow ing localities: 

Allendale, Anderson, 

Batesburg, Brownsville, 

and St. Matthews, S. C. ; 

Chase City, Va.; Macon, 

Ga.; and Albertville and Boaz, Ala. It evidently has a wide distn- 

' TripMeps imidiosui Saj (fig. ID- A small anthocorid bug, 
Triphleps insidi - s Say, was seen as earlj as Maj 16. It is hardier 
than tin- Arthrocnodas and appears earlier in the season. I hrough- 
ont July and August it is extremelj common and both in the 
nymphal and adult stages is second only to the itonid as a red 
spider enemy. Coming upon a red spider, like a flash the adull 

thrusts its sharp proboscis through the pest's back and proc Is 

quietly to siphon out the body contents. The first victim observed 
was "drained" in about five minutes, but each succeeding meal was 
of shorter duration as the appetite became satisfied. The actions 
of the nymph (fig. 12) are similar, but the individuals obsei 
were seen onlv to destroy eggs of the spider. In this operation 




Fn .ii / • ■;■■ "' Impoi 

the red spld Mu< b ■ VuUior's 

lllustral V 



i The 'i ''• ' : '- 



16 



THE RED SPIDER ON COTTON. 



the proboscis was not inserted far into the ovum, and two minutes 
sufficed for draining an egg. 

A species of lace-winged fly {Chrysopa quadripunctata Burin., 
determined by N. Banks) is abundant at Batesburg throughout most 

of the summer, and its larva is doubtless very active in reducing the 
pest. 

Two species of thrips, Euthrips fvscus Hinds and E. occidentals 
Pergande, have been determined this season from cotton. They arc 
commonly found throughout the season about red-spider colonies, 

and may be instrumental in 
spider destruction. Scolo- 
f/irlps sexmaciihitits Pergande 
has been recorded as an enemy 
of the red spider by Pergande 
and by Duffy. 

Lady-beetle larvae and adults 
of several species are com- 
monly seen on infested Leaves, 
These are usually either Coc- 
cinella 9-notata Hbst. or Hip- 
podamia convergent Giut.. 
but a small black species, 
(Scynvrms) Stethorus punctutn, 
Lee. is frequently observed. 
The larger beetles are prob- 
ably more intent upon cotton 
aphides, but the last-mentioned 
species, although later in ap- 
pearing and not overnumerous, seems to be more restricted to the 
the cotton mite than are other species. 




Fig. 12. — Triphleps insidiosus: Nymph. Greatly 
enlarged. (Author's illustration.) 



REMEDIAL MEASURES. 



PREVENTION. 



From the abundant experience of the past two years the writer 
has been forced to the conclusion that the eradication of the red 
spider must be accomplished through preventive efforts rather than 
repressive, if it is to be economically effected. The location of the 
mites through the winter and spring, their preference for the culti- 
vated violet and the pokeweed, and the manner of dispersion of the 
pest lead to the presentation of the following cultural expedients. 

Clean culture. — First among preventive measures against the red 
spider is doubtless that of exterminating the weeds and plants which 
breed the pest. Pokeweed, Jerusalem-oak weed. .Jamestown weed, 
wild blackberry, and all border weeds and underbrush about fields 
should be burned or grubbed out during the winter or early spring. 



I ii E Rl D BPIDEB ON COTTON. 17 

This plan has been tested in several instances and has given complete 
illinium! \ the following season. Too much emphasis can not be 
placed on the importance of destroying, bo far as possible, :ill weed 
growth especially the pokeweed, which should be grubbed out l>\ 
the roots. 

' 'nil i'ii violets. As before stated, most cases "f infestation in 
urban localities have their origin in borders "I" cultivated violets 
growing in near by house yards. In several instances violets adjoin- 
ing fields of past severe annual infestation have been thoroughly 
Bprayed, with the result that no red spiders appeared subsequently 
in these fields. The objection to tin- treatment i- the failure <>n tin 
part of the average person to persevere with the spraying until the 
pests have been entirely exterminated. The m<>-t satisfactory pro 
cedure in such cases consists in the removal and destruction "l the 
( [fending violets, 

Varietal immunity in cotton.— Prom several tests conducted in 
different fields with numerous standard varieties of cotton, and from 
the information volunteered by farmers from many portions of 
South Carolina, data have been accumulated which clearly indicate 
that certain varieties are susceptible t<> red-spider infestation, while 
others exhibit considerable immunity. Careful observations on a 
considerable number of varieties grown for the purpose showed thai 
Dixie "Wilt Proof,*' Toole, Peterkin, Broadwell, and Cook suffer 
most (in the order named) from the attack of the pest, while Kite, 
Russell, Summerour "Half and Half," and Cleveland showed the 
greatest immunity of all the varieties investigated. 

Broadcasted cotton. — An opportunity was accidentally provided of 
testing the value of thickly broadcasting cotton ;it the boundary of 
;i field as ;i trap crop for red spiders. This cotton, intended as ;i 
cover crop, intervened between the cotton field proper and a large, 
heavily infested border of violets -a former abundant source of 
migration. The broadcasted cotton became infested and was later 
plowed in. The adjoining field remained free from mites. The suc- 
cess of this experiment would strongly indicate that the cotton trap 
crop i- a practical cultural expedient to be used in controlling tin- 

pe-t. 

Spacing.— Experiments at Batesburg, S. C, have shown that the 
red spider commonly travels between plant- upon the ground. This 
-how- the futility of spacing as a remedial measure. 

Thm of planting. There i- yet much doubl as to the relative ad- 

vantages of early and late planting. Extremely early planting nat 
urally permit- the plant- to develop a maximum growth of weed 
and fruit by the time of serious mite appearance. It is noticeable 
that plant- of considerable size are rarely hilled by the pe-t. nor are 
well-advanced bolls commonly shed from infestation. On the other 
hand, several field- about Leesville, S. (\. which were planted 



18 THE RED SPIDER OX COTTON. 

late as June 20 seem to have largely escaped the infestation which 
was so general at that locality. Late planting, however, is almost 
universally objectionable to the farmer, since in ordinary seasons it 
results in a reduction of the yield. 

Rotation. — In an effort to test the rotational value of other crops, 
numerous field crops have been planted in or near infested areas. 
In addition, frequent examinations have been made of a great many 
garden and vegetable crop- in infested localities. Besides cotton. 
red spiders are known to occur not at all uncommonly upon the fol- 
lowing field crops: Cowpeas, clover, corn. hops, and watermelon. 
They are also found frequently on the following garden crops: Peas. 
beans, onion, tomato, lettuce, okra. turnip, mustard, squash, beet, 
sweet potato, and strawberry. A really acute infestation on corn 
(as above recorded) was seen at the height of the past season (1912). 
Cowpeas are particularly attractive to the pest, and sweet potatoes 
have been noted to be badly infested. Should an immune crop be 
found and employed, it is extremely probable that the pest would 
reinvade the fields upon the return to cotton culture with as great 
ease and quickness as it has done during any previous season, provid- 
ing the sources of infestation were yet at hand. Rotation, then, does 
not promise to contribute toward the solution of the problem. 

Effects of fertilizers. — A rather elaborate series of tests with fer- 
tilizers has been conducted in an attempt to determine whether the 
various applications assisted cotton to withstand the injurious effects 
of infestation. Since almost no infestation appeared in these test 
plats it was impossible to deduce positive conclusions. 

REPRESSION. 

We have just discussed cultural measures which may help to pre- 
vent infestation. We will now consider what may be done to combat 
the pest when it has already gained entrance to a Held. 

The writer believes in prevention rather than cure, in the case of 
the red spider. When once well established in a cotton Held the 
pest is a most difficult one to wipe out. That it is possible, however, 
to eradicate the pest from infested fields has been demonstrated be- 
yond doubt, but in many cases the task i- so tedious that only the 
most determined farmers will undergo the effort necessary to accom- 
plish the extermination. 

ll< moral of infested plants. — The experiment ha- been thoroughly 
tested of pulling up ami destroying the Hist few plant- which show 
infestation. In such cases the operation was repeated several times. 
Great care was observed in locating every plant showing the charac- 
teristic red spots, and these were carefully taken from the Held and 
burned. If infestation has not advanced far. this treatment is 
usually satisfactory, and a red-spider invasion often may be " nipped 
in the bud " and entirely eradicated. 



Mil RED -rihi i: ON COTTON. 



19 



[f infestation has spread until a considerable patch has become 
involved ii is Bometimes advisable, in the case "I" a large field, t" plow 
up nil the affected portion in order i" Bave the balance of the field. 
Such ;i drastic measure, however, should orilj be resorted to in es 
treme cases, and the planter concerned must l>e the j 1 1 « I i-r * • oi 
;nl\ isability. 

Occasional observations <>l" instances wherein infestation had 
abruptly stopped ;it ;i much-traveled road suggested the idea of plow- 
ing a wide swath just outside the boundary of infestation. This 
attempted in one case where the occurrence had covered aboiil 2 
acres. A LO fool ring was plowed around the spot, and all stalks, 
both in the swath and in the inclosed area, were immediately burned. 
Unfortunately the farmer did n<»i make sure thai he was beyond the 
outermost /.one of infestation, and consequently ;i sufficient number 
of affected plants remained outside the pulverized barrier to con- 
tinue, somewhat, the dispersion of the pest. This idea should be 
given further tests, as it seems there should be great efficacy in the 
operation, provided the swath i- kepi stirred frequently. 

Insecticides. During the season <>f L911, 26 spraj combinations 
were thoroughly tested under conditions entirely natural. The field 
used for this purpose was aboul 1 acre in extent, and infestation had 
become both very genera] and very severe. A strip through the mid- 
dle of the field, crossing each sprayed plat, was lefl unsprayed t<> 
serve as m check. Since do substance was discovered which could be 
safely used to destroy all eggs in one application, it was found nei 
sary t<> spray twice, with an interval of six or se 1 en days, so as t" de- 
stroy tlu> hatching larva;. The killing ability of all these sprays was 
computed, and the percentages ranged from I 1111 to 0. Each of the 
following six combinations (see Table IV) was found to be very 
satisfactory. These are presented to indicate the manner of prepara- 
tion, together with the cost, of LOO gallons <d" each. 

TABl I \ ■tins! th( /< /■. 












i 
ii 

in 

IV 
V 

VI 



lions. 
Flowers of sulphur | 

timi ...| I 

" 

" 

Blacklral tol .unccs, at * 

:; ! 
•■ U) 111 l^'' 101 

Flowers of sulphur. X . $1.12 

per pourj i 
Water to m 



JO 75 



1 40 



100 
100 



- 



20 THE RED SPIDER OX COTTON. 

In the course of spraying tests against the red spider on hops in 
California, conducted by Mr. W. B. Parker. 1 of thi- bureau, it seems 
to have been demonstrated that Hour paste, used alone or combined 
with caustic materials, is a valuable acaricide. The function of the 
flour paste appears to be twofold: Used alone it glues the tiny mites 
to the leaves, and when added to lime-sulphur, or other solutions, it 
serves as a spreader to prevent the spray film from breaking up into 
"• I icads " as it dries on the leaf. Mr. Parker recommends the follow- 
ing formulas : 

I. Stock solution of flour paste. 

Mix cheap wheat flour with cold water at the rate of 1 pound of flour 
to 1 gallon of water. Boil to a paste. 
II. Flour-paste spray. 

Use 8 gallons of the above stock-solution paste to each 100 gallons of 
water. Keep constantly agitated while spraying. 
III. lime-sulphur and flour-paste mixture. 

Use 4 gallons of flour-paste stock solution to each loo gallons of lirne- 
sulphur spray. 

During the recent season no serious effort was made to test addi- 
tional insecticides. Further use of the sprays mentioned, however, 
seems to establish the superiority of potassium sulphid, lime-sulphur 
solution, and miscible-oil-tobacco solution. The last preparation 
seems to possess better lasting qualities than the others, since, in the 
absence of rain, one application will also suffice to kill a certain per- 
centage of the hatching larva?. If one of these were to be used in 
preference to all others, it would probably be potassium sulphid. 
This insecticide commends itself from every standpoint — cheapness, 
simplicity of preparation, ability to kill quickly, and safety of foliage. 
Altogether it seems to be an ideal red-spider spray. It was found 
that 100 gallons, wdien applied as a mist spray, about sufficed to treat 
an acre of average-sized cotton. 

Spraying out-fits. — The sort of outfit to be used for red-.-pider 
s{3raying depends mainly upon the extent of the occurrence. Some 
have sprayed their score or so of affected plants with a 75-cent tin 
atomizer. While this instrument is very economical of liquid and 
throws a misty spray which penetrates and blows to all parts, it is 
not economical of time. The bucket pump and knapsack pump come 
into use in cases of considerable scattered infestation or for the 
treatment of a few high plants. The most economic outfit for a 
severe case involving several acres consists of a barrel pump carried 
through the field on a wagon. One man drives, one pumps, and one 
handles each sprayer (of which preferably there should be two). 
Thorough treatment of 3 or -1 acres per day is readily obtainable with 
this device. For safe work, however, this outfit should 1m? used only 

1 Flour pnstp as a control for red spiders and as a spreader for contact insecticides, 
Clr. IOC. Bur. Ent, T". S. Dept. Agr., January 30, 1913; The rod spider on hops in the 
Sacramento Valley of California, Bui. 11", Bur. Ent., D. S. Dept. Agr., 1913. 



Ill B BSD BPIDBB ON COTTON. 2 1 

on cotton of average or loti Bize, as the passing wagon will injure 
large plants. 

\ ' i/ for thorough spraying. Some dissatisfaction has been 

experienced among certain of those who have undertaken to check 
the ravages of the red spider l>\ spraying. This can be understood 
on account of the extreme care which must be exercised in order to 
secure effective results. In the case of insects which devour the plant 
tissue even the careless application of Paris green or lead arsenate to 
the top of the foliage is often effective. Tin- is explained by the fact 
that such pests are constantly moving from leaf t" leaf and will 
eventually eat some of the poisoned tissue. Moreover, these insects 
often eat entirely through the leaf, and In 'net' it mat in-- little whether 
the poison falls upon one side or the other. With the red spider, 
however, it is altogether different. A contact insecticide is absolutely 
necessary, and, from the fact that the mite as a rule passes it- entire 
existence upon the underside of a single leaf, it becomes plainly 
necessary in spraying to hit tin entire undersidi of < very l<'ii of an 
infested plant. It is obvious, therefore, thai indifferent spraying is 
certain t<> yield unsatisfactory results. Furthermore, the absolute 
necessity for a second spraying to kill the hatched eggs add- to the 
difficulty. 

It i- hoped that this discussion may impress upon the reader tin 
• i<r- r, ntion of iii festal ion. 

-t mm w:> . 

The female red spider, appearing to the naked eye like a dot of 
reddish ink from the point of a fine pen, lays about 50 or 60 round, 
colorless eggs, which hatch in summer time in about four day-. 

The colorless, newborn spider has six legs, \'rv<\^ at once, and molts 
in two day- to the primary nymph. 

This first nymphal stage (and all later stages) possesses eight legs, 
and ha> become larger in size and darker in color. In two more days 
t in summer) it. in turn, molts to the secondary nymph. 

The second nymphal stage lasts two day-, at the end of which time, 
after molting, the fully formed adult emerges. Mating occur- at 
once and egg laying commences immediately afterward-. 

Thus one generation requires in summer weather in South Caro- 
lina about K> or 11 day-. There are probably about 16 or 17 genera- 
tions in an average year iii that locality. 

The red-spider colonies live on the underside of the cotton leaves, 
and their constant feeding causes hlood-red spots to appear on the 
top- of the leave.-. The effect upon the cotton plant is that the leaves 
drop, one by one. until usually the plant •lie-. 

The pe-t increases and spreads most rapidly in hot. dry weather 
until (toward the end id' August I -evcral acre- of a field may become 
badly damaged. 



UNIVERSITY OF FLORIDA 



22 



THE BED SF1DBB OH C< , j| ,l !J^ ll 2 i 'S^^'e""/^^ 

Several insects have been discovered which destroy many mites 
and are thus of great benefit to the planter. 

At the end of the cotton-growing season most of the red spiders 
migrate afool in search of greener plants. The majority of those 
which arc destined to survive the winter probably settle on either the 
cultivated violet or on the pokeweed. 

RECOMMENDATIONS. 

(/) Clean culture.— Destroy, by burning and grubbing out, all 
weed, and underbrush about cotton fields, being especially careful to 
remove all pokeweed. Practice fail plowing so far as possible, 

(2) Control on violets.— Destroy or thoroughly spray cultivated 
violet plants which may he growing near cotton field-. 

(S) Resistant varieties. — In choosing seed for the crop avoid varie- 
ties which suffer most from red-spider attack. 

( .',) Broadcasted trap borders. — Thickly sow cotton along margins 
of fields at points where infestation has appeared on former occasions 
and plow these in about dime 1. so as to intercept and destroy the in- 
vading mites. 

(5) Putting -first infested stalks.— Maintain a careful watch of 
fields from the time of the earliest appearance of cotton above ground, 
so that the first attacked plant- may he detected, removed, and burned, 
thus preventing further spread. 

{6) Barrier strip.— In case a considerable area of cotton has be- 
come affected before discovery, remove and burn the worst of it and 
then plow a 10- foot -trip completely around the extreme outside of 
the infested area. Keep this strip stirred frequently to make further 
dispersion difficult. 

(7) Spraying.— Apply one of the insecticides recommended to the 
infested portion of a field before infestation becomes too general to 
prohibit its use. Choose the pump outfit which hot suits the par- 
ticular case. Two application- should be made. The second, a week- 
after the hist, i- to kill the individuals which were eggs at the time of 
the first spraying. 

Unlike many other pests, the red spider has no wings and spreads 
mainly by means of its tiny legs. Migration doe- not extend far from 
its winter quarters. This makes every man'.- problem virtually his 
own. In other word-, if his infestation always come- from a certain 
spot upon his premises, proper attention to this -pot will yield him 
satisfactory results in spite of the negligence of hi- neighbors. 

Approved : 

Jambs Wilson, 

Secretary of Agriculture. 
Washington, I). C. January ..'.J. WIS. 

O